Ultrasonic treatment apparatus

ABSTRACT

In an ultrasonic treatment apparatus the tank adapted to hold the liquid is made of material having a relatively low thermal conductivity, such as polymeric plastics. The transducers are mounted by a first resinous material to a metallic plate which in turn is mounted by a second resinous material to an outer surface of the tank. The first resinous material (epoxy) has a curing temperature which is higher than that of said second resinous material. The plate is provided with spacing means to cause a predetermined thickness of said second resinous material.

Fuller et a 21%? 3 a 76 s l 1.55

United ULTRASONIC TREATMENT APPARATUS Inventors: David H. Fuller, Huntington;

Herman A. Rissolo, Norwalk, both of Conn.

[73] Branson Instruments, Incorporated,

Stamford, Conn.

Filed: Feb. 28, 1972 Appl. No.: 229,952

Assignee:

[52] US. Cl 259/72, 156/309, 156/330, 3l0/9.1

[51] Int. Cl. B011 7/02, C09j 5/04, C09 5/06 259/DIG. 44; 68/3 SS; 134/1, 184; 156/309,

330; 3lO/9.l, 9.2, 9.3, 9.4

References Cited UNITED STATES PATENTS Carmichael 259/1 R Field of Search 259/1 R, 72, DIG. 41,

[451 Oct. 9, 1973 3,700,937 10/1972 Rissolo 259/D1G. 44 X 3,596,883 8/1971 Brech 134/184 X 3,627,278 12/1971 Dee et a1. 259/72 Primary Examiner-Billy .1. Wilhite Assistant ExaminerAlan I. Cantor Attorney-Ervin B. Steinberg 57] ABSTRACT In an ultrasonic treatment apparatus the tank adapted to hold the liquid is made of material having a rela tively low thermal conductivity, such as polymeric plastics. The transducers are mounted by a first resinous material to a metallic plate which in turn is mounted by a second resinous material to an outer surface of the tank. The first resinous material (epoxy) has a curing temperature which is higher than that of said second resinous material. The plate is provided with spacing means to cause a predetermined thickness of said second resinous material.

13 Claims, 4 Drawing Figures ULTRASONIC TREATMENT APPARATUS BRIEF SUMMARY OF THE INVENTION This invention refers to an apparatus for treating articles, particularly cleaning or etching, by immersing such articles in a solution which is agitated by sonic or ultrasonic energy. More particularly, this invention refers to a simplified arrangement for providing a sonically or ultrasonically agitated etchant, or other highly corrosive or chemically active liquid.

A novel treating arrangement using a tank made of polymeric plastics material for containing an etchant solution ahd having acoustically coupled thereto one or more ultrasonic transducers is shown in U.S. Pat. No. 3,405,916 entitled Ultrasonic Treatment Apparatus issued to John J. Carmichael on Oct. 15, 1968, which patent is assigned to the assignee of this application. As disclosed in that patent, special techniques are required for coupling the transducer in vibratory energy transmitting contact with an outside surface of such tank. The particular problem to be solved resides in the provision of means for conducting heat away from the interface area between the transducer and the tank. The plastic tank has a relatively low thermal conductivity and, unless the heat is conducted away from the area of transducer attachment, a softening and melting of the thermoplastic material occurs, such heat being produced by the dissipation of vibratory energy.-

Since it is common practice to attach transducers to the treatment tank by resinous material, such as epoxy resin, the aforementioned patent discloses various thermal conductive means which can be interposed in the bond between the transducer and the tank for conducting heat out of the joint area.

Typically, a metallic plate, a metallic screen or metallic powder is disposed in the area of transducer attachment and extended to the area beyond such attachment where standard cooling processes remove the heat.

The present invention is directed toward an improved arrangement and, while using the techniques described in the above stated patent,'the instant disclosure describes certain features which provide a more reliable tank construction and reveals also the manufacture of a transducer subassembly which is attached to the tank as a unitized assembly.

A principal object of this invention is, therefore, the provision of an ultrasonic treatment apparatus comprising a chemically inert tank and a subassembly of one or more ultrasonictransducers which assembly is attached to the tank in a unitary manner.

Another important object of this invention is the provision of a tank made of material having a relatively low thermal conductivity and fitted with one or more ultrasonic transducers, including means for improving the quality and reliability of such transducer attachment.

Another and further object of this invention is the provision of an ultrasonic cleaning tank made of polymeric plastics material which is fitted with a plurality of ultrasonic transducers and which includes means for improving the method of attaching the transducers to an outside surface of the tank.

Further and still other objects of this invention will be more clearly apparent by reference to the following description when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. 1 is an elevational view, partly in section, of a preferred embodiment of the present invention;

FIG. 2 is an enlarged view, illustrating the construction of transducer attachment;

FIG. 3 is a sectional view of a portion of the attachment plate showing typical spacing means, and

FIG. 4 is a sectional view of a portion of the invention, illustrating the attachment of a heat protective device.

DETAILED DESCRIPTION Referring now to the figures, and FIGS. 1 and 2 in particular, there is shown a tank 12 containing a solu' tion 14, typically an etchant for treating, for instance, small semiconductor parts. The tank 12 in a typical example is made of /4-inch thick polyvinyl chloride or polypropylene material. The bottom of the tank is fitted with one or more ultrasonic transducers 16 which are adapted to receive high frequency electrical energy and provide in response thereto sonic energy, preferably in the ultrasonic frequency range, to the solution 14 by transmission through the bottom of the tank 12.

Typically, each transducer 16 is made of the clamped sandwich construction and includes one or more disks of piezoelectric material. Transducers suitable for this purpose are shown in detail in U.S. Pat. No. 3,066,232

trasonic Transducers."

The transducers 16 are mechanically coupled to the underside of the tank bottom in such a way as to assure removal of heat caused by the dissipation of sonic energy at the interface between the transducer 16 and the tank 12. This feature is particularly important since plastics material of the type described above and other chemically inert material, such as ceramic or glass, have a relatively low thermal conductivity.

With special reference to FIG. 2 the transducers l are attached by a suitable resinous bonding material 20, such as epoxy; resin to a metal plate 22 which, for instance, may be a flat aluminum plate one-sixteenth inch thick. The resinous material, quite suitably, is a commercial resin, such as No. Ht 424 available from the American Cyanamid Company. This resin material comes in sheet or film form, is cut to size and then is interposed between the transducer frontal surface and oneside of the aluminum plate 22. Using a suitable clamping pressure between the transducer 16 and the plate 22 the epoxy resin 20 is cured by baking at a temperature of approximately 350F. The above procedure produces a unitary subassembly which comprises the plate 22 having attached thereto at one side one or more transducers 16.

Following the above step, the plate 22 is bonded to an outer surface of the tank 12, such as the bottom surface of the tank. Most suitably, another resinous bonding material 24 is used, such as epoxy resin No. BR 92 contraction of the metal plate 22 during cooling will cause excessive shear stresses between the plate and tank surface resulting in shearing of the metal plate 22 from the tank surface.

In addition, it has been found most desirable for the purpose of increasing adhesive strength to interpose spacing means between the plate 22 and the tank surface. Such spacing means provide a predetermined bond thickness of the epoxy layer 24. It will be appreciated that if this bond thickness is too large, the transmission of vibratory energy from the transducer to the tank is impaired and conversely, if the bond thickness is too thin, as may be caused by displacement of the fluent resinous bonding material under the influence of pressure, the adhesive strength of this bond is insufficient. Most suitably, the plate 22 is provided with a set of punched holes, such as three thirty-seconds inch diameter holes, in which eyelets 26 are fastened. The holes for the eyelets are punched at areas outside of the transducer attachment area, e.g. at the interstices between the transducers. Using standard eyelets as are commercially available a predetermined bond thickness of about 0.014 inch can be assured.

In addition, it has been found most advantageous to disperse in the resin material 24 when still fluent metallic powder particles, such as aluminum powder. Suitable powder is available under the trade name Valimet 817 from the Valley Metallurgical Company,

Haskell, New Jersey. In a typical example aluminium powder of 250-350 mesh is dispersed in the soft epoxy resin prior to adding the hardener. The metallic powder dispersed in the resin improves the heat transfer from the interface between the tank surface and the metal plate and enhances, moreover, the acoustic energy transmission.

As seen in FIG. 4 a thermostat 28 is fastened to the plate 22 by means of a set of studs, spot-welded to the plate, and nuts 30 to provide a heat responsive cut-out when the temperature of the plate 22 exceeds a predetermined temperature level. The thermostat, when actuated, is used to disable the generator (not shown) which energizes the transducers 16 as is known to those skilled in the art. A skirt 32 is used to support the tank 14 with transducers coupled thereto, and a cooling fan 34 inside the skirt and fastened thereto may be used to provide forced air cooling to assure improved heat removal.

For large tanks, it will be found advisable to use several metal plates 22, each such plate being fitted with one or more transducers 16. An arrangement of this type minimizes the shear stresses produced as the result of the difference of the coefficient of expansion between the metal plate and the non-metallic tank surface.

The construction set forth in detail above, as is apparent, provides certain improvements over the design described in the earlier patent. It should be understood that the specific tank material, metal plate material, resinous material, etc. disclosed are merely illustrative of a preferred arrangement which provided excellent results, but it shall be clearly understood that such data in no way shall be interpreted as limiting the disclosure. Other materials and combinations may be used to achieve substantially the same result and the invention shall be limited only by the scope of the appended claims:

What is claimed is:

1. An apparatus of the type comprising:

a tank made of material having a relatively low thermal conductivity adapted to hold a liquid to be agitated by sonic energy;

a metallic plate;

at least one transducer adapted to receive electrical energy and provide sonic energy at a frontal surface thereof;

a first resinous bonding material bonding the frontal surface of said transducer to one side of said plate;

a second resinous bonding material bonding the other side of said plate to an outside surface of said tank, and

spacing means interposed between said plate and said outside surface of said tank for spacing said other side of said plate a predetermined distance from said outside surface to cause a predetermined thickness of said second resinous bonding material to be interposed between said plate and said tank.

2. An apparatus of the type as set forth in claim 1, said first and second resinous bonding material being heat curable, and said first resinous bonding material having a curing temperature which is higher than that of said second resinous bonding material.

3. An apparatus of the type as set forth in claim 1, said second resinous bonding material having dispersed therein metallic powder particles.

4. An apparatus of the type as set forth in claim 3, said plate being made of aluminum and said metallic powder being aluminum powder.

5. An apparatus of the type as set forth in claim 1, said spacing means comprising eyelets anchored in apertures of said plate.

6. An apparatus of the type as set forth in claim 5, said plate being provided with a plurality of transducers, and said eyelets being disposed at interstices between said transducers.

7. An apparatus of the type as set forth in claim 1, said tank being made of polymeric plastics material, and said one side of the metallic plate supporting a plurality of said transducers.

8. An apparatus of type as set forth in claim 7, said first resinous bonding material and said second resinous bonding material comprising epoxy.

9. An apparatus of the type as set forth in claim 8, said metallic plate being aluminum.

10. The method of attaching ultrasonic transducers to a tank made of material having a relatively low thermal conductivity and which is adapted to hold a liquid to be agitated by ultrasonic energy comprising the steps of:

providing a metallic plate; disposing at least one ultrasonic transducer on one side of said plate and placing a first heat curable resinous bonding material between said transducer and said one side;

curing said first resinous bonding material at a first temperature;

disposing the other side of said plate with said transducer attached to said plate on an outside surface of said tank and placing a second heat curable resinous material between said plate and said tank, and

curing said second resinous bonding material at a temperature which is lower than said first temperature.

11. The method as set forth in claim 10, said tank being made of polymeric plastics material.

12. The method as set forth in claim lll, said first bonding material being cured by heating at a temperature above 200 degrees F, and said second bonding material being cured by heating at a temperature below 200 degrees F.

13. An apparatus of the type comprising:

a tank made of material having a relatively low thermal conductivity adapted to hold a liquid to be agitated by sonic energy;

a plurality of metallic plates;

a plurality of transducers, each such transducer second bonding material. 

2. An apparatus of the type as set forth in claim 1, said first and second resinous bonding material being heat curable, and said first resinous bonding material having a curing temperature which is higher than that of said second resinous bonding material.
 3. An apparatus of the type as set forth in claim 1, said second resinous bonding material having dispersed therein metallic powder particles.
 4. An apparatus of the type as set forth in claim 3, said plate being made of aluminum and said metallic powder being aluminum powder.
 5. An apparatus of the type as set forth in claim 1, said spacing means comprising eyelets anchored in apertures of said plate.
 6. An apparatus of the type as set forth in claim 5, said plate being provided with a plurality of transducers, and said eyelets being disposed at interstices between said transducers.
 7. An apparatus of the type as set forth in claim 1, said tank being made of polymeric plastics material, and said one side of the metallic plate supporting a plurality of said transducers.
 8. An apparatus of the type as set forth in claim 7, said first resinous bonding material and said second resinous bonding material comprising epoxy.
 9. An apparatus of the type as set forth in claim 8, said metallic plate being aluminum.
 10. The method of attaching ultrasonic transducers to a tank made of material having a relatively low thermal conductivity and which is adapted to hold a liquid to be agitated by ultrasonic energy comprising the steps of: providing a metallic plate; disposing at least one ultrasonic transducer on one side of said plate and placing a first heat curable resinous bonding material between said transducer and said one side; curing said first resinous bonding material at a first temperature; disposing the other side of said plate with said transducer attached to said plate on an outside surface of said tank and placing a second heat curable resinous material between said plate and said tank, and curing said second resinous bonding material at a temperature which is lower than said first temperature.
 11. The method as set forth in claim 10, said tank being made of polymeric plastics material.
 12. The method as set forth in claim 11, said first bonding material being cured by heating at a temperature above 200 degrees F, and said second bonding material being cured by heating at a temperature below 200 degrees F.
 13. An apparatus of the type comprising: a tank made of material having a relatively low thermal conductivity adapted to hold a liquid to be agitated by sonic energy; a plurality of metallic plates; a plurality of transducers, each such transducer adapted to receive electrical energy and provide sonic energy at a frontal surface thereof; a first resinous bonding material bonding the frontal surface of a respective transducer to one side of a respective plate of said plurality of metallic plates; a second resinous bonding material bonding the other side of said plates to an outside surface of said tank, and said first resinous bonding material being selected to have a higher curing temperature than that of said second bonding material. 